DISTRIBUTION OF MYXOMYCETES 391 



DISTRIBUTION OF MYXOMYCETES 



Collectors of Mvxomycetes are quite universally inclined to 

 the opinion that this group is among the most ubiquitous and cos- 

 mopolitan of organisms. Intensive collecting, even in restricted 

 areas at widelv distant points, has yielded for each locality only 

 from one-third to one-half of all the species known throughout 

 the world. Nevertheless the geographical distribution of slime 

 molds is not fortuitous but depends upon such dominant factors 

 in each locality and for each species as temperature, moisture, 

 kind of substrate and its acidity or alkalinity, and other factors. 



More species of slime molds have been recorded for temperate 

 regions than for the tropics, but this phenomenon appears to be 

 causally related to the greater interest in collecting in the tem- 

 perate zones. Some species, however, are limited to temperate re- 

 gions; others, such as Trichamphora pezizoides and Alwisia bom- 

 bar da, to tropical or subtropical regions [Martin (1940)]. This 

 observation need not necessarily be interpreted as proof that tem- 

 perature is the primary and controlling factor in determining the 

 range of slime molds in general. Otherwise it becomes difficult 

 to explain numerous observations like those of Smith (1931), who 

 noted that in Colorado species of Badhamia prefer decaying aspen 

 or cottonwood logs, whereas species of Cribraria are restricted 

 to coniferous wood. As a result of several years' experience in 

 collecting slime molds, Smith (1931) concluded that moisture, 

 especially adequate rainfall for considerable periods, is the primary 

 desideratum for their growth, the proper kind of decaying vege- 

 table matter being; secondary. He correlated the Greater rainfall 

 at elevations of 8000 to 9000 feet in Colorado with the greater 

 abundance of species. Even though he collected Stemonitis fusca, 

 Comatrichia nigra, and several species of Cribraria and Arcvria on 

 dry exposed slopes, they invariably were found only on the lower 

 side of logs kept moist by melting snow. The fact that the lower 

 side of logs is preferred by slime molds is not regarded as a re- 

 sponse to gravity, an opinion on which there is general accord. 

 Smith (1931) and MacBride (1914) do not contend that any of 

 the species they collected in the high mountains near the timber 

 line are alpine. 



